Alginate Hydrogel Micro-Motors Produced By Hydrodynamic Electrospray Ionization Jetting And Its Magnetic Propulsion

The hydrodynamic electrospray ionization jetting method(HESIJ)is an important method for preparing hydrogel particles and capsules.HESIJ has many applications.First,HESIJ has been widely used in the field of analytical chemistry as an ionization method used in electrospray ionization mass spectrometry(ESI-MS)and ion mobility spectrometry(ESIIMS)and its combined techniques(such as ESI-IMS-MS).The gentle nature of the ionization process does not destroy the analytes that need to be ionized(such as biomolecules,like proteins).Secondly,HESIJ has the advantages of simple experimental equipment and low construction cost.Finally,HESIJ is highly efficient in the preparation of hydrogel particles or capsules.A large amount of particles or capsules can be quickly produced in a few seconds,by applying a high voltage to the electrospray needle and starting the syringe pump to deliver the electrospray solution.In the present thesis,the HESIJ method was optimized and improved for the production of alginate hydrogel particles and capsules by using the natural polymer sodium alginate as raw material and divalent calcium ion or copper ion as cross-linking agent.The HESIJ experimental parameters were optimized to investigate the mechanism during the electrospray process.Further,calcium alginate particle and capsule micro-motors were prepared by integrating magnetic nanoparticles,and their magnetic driving motion were realized.The present thesis reported the following academic research work:For the preparation of hydrogel microparticles in the existing HESIJ method,the electrospray modes are less investigated(mainly conejet mode).The experimental parameters,such as electrospray mode,spray distance and electrospray solution concentration were investigated.Calcium cross-linked alginate hydrogel particles are prepared by the HESIJ method.The electrospray dripping mode and the multijet mode have been systematically studied.This work has shown that alginate hydrogel particles are showing differences in the diameter and aspect ratio in three electrospray modes(drop,cone and multi-spray modes),four spray distances(5,10,15 and 20 cm)and six spray concentrations.Comparing the three electrospray modes,the conejet mode produces hydrogel particles with the smallest particle size and the lowest aspect ratio.For all electrospray modes,the particle diameter formed is independent of the spray distance when the spray solution concentration is ? 2.5%.In different electrospray modes and spray distances,the aspect ratio of the particles is significantly different.When the concentration of sodium alginate solution is ? 1.5% and the spray distance is 20 cm,the aspect ratio of the particles produced by all electrospray modes gradually increases.This phenomenon can be explained by the chain ejection model.A method for preparing alginate hydrogel particles by ultrasonic assisted HESIJ was studied.When the hydrogel is sprayed onto the surface of the liquid,a surface saturation effect occurs,forming a growing hydrogel layer until the formation of the hydrogel particlesis terminated.The use of ultrasonic waves can effectively prevent surface saturation effects during electrospray preparation of hydrogels.The effects of spraying distance,electrospray mode,alginate concentration,ultrasonic frequency and shape of electrode on the size of hydrogel micro-nanoparticles were systematically investigated.The alginate hydrogel micro-motor was successfully prepared by integrating biocompatible magnetic nanoparticles in the electrospray preparation process.The micro-motor can be autonomously driven by a rotating magnetic field with a strength of 5 mT to 20 mT and a frequency of 1 Hz to 100 Hz.These rotating alginate hydrogel micro-motors can be oriented in solution and have potential applications in drug delivery.Sodium alginate electro-sprayed under the condition of a negative charging potential is leading mainly to the production of compact hydrogel particles.Hollow capsules are more difficult to produce in the negative charging electrospray modus.On the other hand,the ion exchange of sodium to the cross-linking calcium is strongly favored for alginate in the negative spray mode,considering the molecular structure of alginate.According to this condition,the next approach is gained by the production of biodegradable alginate capsules cross-linked by calcium,which are made by hydrodynamic electrospray ionization with the assistance of low frequency ultrasound.Recently introduced polyelectrolyte complex capsules produced by spraying are non-biodegradable and not biocompatible,which limits their practical application.The size and shape of most calcium alginate capsules show significant differences with respect to different spraying distance,spraying mode,electrode shape,and spraying concentration.Hydrogel microcapsule shapes such as vases,mushrooms and spheres were successfully prepared by adjusting the experimental parameters,and the average size was adjustable in the range of 10 ?m to 2 mm.These microcapsules can be used to load drugs.The micro-capsules can be converted into alginate hydrogel micro-motors after incorporating magnetic nanoparticles in the capsule shell.Encapsulated magnetite nano-particles enable defined directional motion under the propulsion of a rotating magnetic field,while model drugs can be released by ultrasound irradiation.